10 micron nominal is the old way to size filters (1960s). Absolute micron is better (1970), but the best way is by a Beta rating (late 70s). I would guess a 10 micron nominal filter is about a 20 to 25 absolute micron filter, but they can vary a lot.
Note that red corpules in your blood is 8 micron in size. To affect additives in an
oil, filters would have to be well below 1 micron, about .1 micron or smaller would be my estimate.
Lee